The main components of a drive-train are a drive assembly and a transmission. The transmission converts rotational speeds and torques, and so transmits a traction force delivered by the drive assembly to a drive output of the drive-train. The present invention concerns a method for operating a drive-train with a drive assembly in the form of a hybrid drive, such that a clutch is connected between the internal combustion engine of the hybrid drive and the electric machine of the hybrid drive. A drive-train to be operated in accordance with the method according to the invention also comprises a primary retarder or a secondary retarder, a primary retarder being one that is connected between the electric machine of the hybrid drive and a transmission input of the transmission whereas a secondary retarder is connected between a transmission output of the transmission and the drive output of the drive-train.
To ensure proper operation of a drive-train, hydraulic oil, which is supplied to the transmission of the drive-train or to other assemblies thereof, must be at a minimum temperature. The present invention for operating a drive-train relates to details of how the hydraulic oil of such a drive-train can be warmed up rapidly to a minimum temperature.
From DE 103 42 893 A1 a method for warming up hydraulic oil in a transmission oil circuit is known, in which, to warm up the oil in the oil circuit, a power loss is produced whose heat is used to warm up the hydraulic oil.
From DE 199 34 621 B4 a circuit system of a retarder is known, with the help of which heated oil can be used immediately after the retarder to warm up transmission oil directly.